Inkjet recording methods have become rapidly popular in these days because of their capability of easy recording of color images and advantages of low running costs. However, the inkjet recording methods have problems that image defects typified by character feathering easily occur depending on the combination of an ink with a recording medium used, which leads to large degradation in image quality.
For example, when a coated paper using, as a coating layer material, a filler which is inexpensive and has high concealability and a relatively small amount of absorption, such as calcium carbonate and kaolin, like coated paper for commercial printing or publication printing, is used as an inkjet recording medium, the resulting image sometimes suffers from ink bleeding and insufficient image density. This is because, unlike inkjet exclusive recording paper, coated paper is not designed to absorb a large amount of ink for a short time, and thus such ink feathering results from absorption delay, and even if ink is absorbed into a coating layer of the coated paper, a coloring material of the ink is concealed by a filler having high concealability like kaolin, which is contained in the coating layer. Accordingly, it has been believed that paper of this type is not suitable for inkjet recording.
Meanwhile, with respect for inkjet inks, in recent years, attention has been focused on aqueous pigment inks, in which a pigment serving as a coloring material is formed into fine particles and dispersed in water, in terms of their high image density, high storage stability after recording and their high waterfastness. Pigments of this type are now expected that the texture of prints can be made closer to those of commercial prints, because the composition of the coloring material is similar to those used in general commercial printing. However, when a pigment ink is used to perform recording on a coated paper for commercial printing or publish printing, the following problems arise: the coated paper suffers from ink absorption delay and causes image bleeding, the ink is not fixed after being dried, and the formed image does not exhibit glossiness.
To solve the above-mentioned problems, there has been proposed a recording method in which a combination of a pigment ink having high permeability with a recording medium having low ink absorptivity is used (see PTL 1). According to this proposed recording method, a small amount of a pigment ink having ultra-high permeability is used to be printed on a recording medium provided with a coating layer designed to suppress ink absorption properties (permeability) so as not for the coloring material in the ink to penetrate therethrough as much as possible. By making only solvents (water and organic solvent) forming the ink selectively penetrate through recording medium, only the coloring material (pigment) is efficiently retain on the surface of the recording medium without using a specific material like a cationic fixing agent. In addition, since a sufficient image density can be obtained with a small amount of ink, superior ink dryness can be obtained. Further, by making the pigment in the ink retain on the surface of the recording medium, the transparency of layers in the recording medium that the conventional recording media are required to have as a necessary function has become indispensable.
Meanwhile, when commercial printing or publish printing is performed, in most of cases, at least several hundreds sheets to several thousands sheets of paper are necessary to be output at a time, and also, printers are required to continuously and stably output images without image defects. When an inkjet printer is used for such purposes, what is really acknowledged as a problem is images streaks nozzle clogging due to dry of ink and due to bended ejection angles of nozzles, caused by adhesion of dried ink around the nozzles. The most effective method to prevent this phenomenon is to add a water-soluble organic solvent having a high boiling point in ink, thereby preventing the ink from being drying.
Here, in the method discussed in PTL 1, when a combination of a recording medium having extremely low ink absorption as seen in commercial printing paper with an ink into which a water-soluble organic solvent, which is highly efficient in preventing printer heads from drying (nozzle clogging) and having a high boiling point, is used, there is a disadvantage that it takes a long time to not have ink bleeding (called “ink adhesion”) even if the ink looks dried and the recording medium is rubbed. This is because a coloring material remaining on a surface layer of the recording medium is wetted for long hours with containing a small amount of a wetting agent. This phenomenon similar to that of the case where an offset ink using a soybean oil needs to have long hours until it is fixed after being printed. Therefore, when an inkjet recording is performed for the purpose of commercial printing according to the method disclosed in PTL 1, it takes a long time to be fixed on a recording medium, and the method is inferior in convenience, for example, prints are intended to be distributed as flier or catalogue shortly after printing, the method cannot be respond to the need.
In order to improve the dryness and fixability of inkjet recorded matters immediately after being printed, it is proposed to use a heating roller as a drying auxiliary unit to dry such inkjet recording matters (see PTL 2). However, in the case of using an inkjet recording method, when a printed matter is dried by heating, a large amount of water contained in an ink becomes water vapor to fill in the machine, easily causing problems such as condensation, bite (corrosion), and the like.